1. Field of the Invention
The present invention relates to multilayer, co-extruded, ionomeric thermoplastic sheet and film, articles manufactured with a decorative surface of such sheet and film, and processes for making shaped articles having a top surface of decorative ionomeric film.
2. Description of the Related Art
To describe the background of the present invention in this section and various components used in the invention, various patents are referenced. Each of these patents is incorporated herein by reference.
There is an increasing need, particularly in the automotive industry, for panels and parts made of polymer materials. Use of such polymer panels and parts provide numerous benefits. For example, weight of the finished assembly is reduced (important for automobiles), capital costs associated with plastic are lower than with metal, styling freedom is increased (important in automotive industry where there are more and more model demands), and manufacturing (plastic tooling) costs are lowered.
Use of such parts and panels, however, has been limited by various problems. Typically, polymer surfaced panels do not present a surface appearance comparable to a high quality automobile finish or do not provide a good bonding surface for the paints needed to achieve the high quality finish. Furthermore, high quality painting can be costly and present significant environmental, as well as safety and health problems, particularly those associated with volatile organic carriers used in paints. Other concerns with polymer parts include suitable properties and durability of those properties with extended outdoor exposure, including high gloss appearance, impact strength, high temperature properties (e.g. tensile strength and dimensional stability), low temperature properties, durability, scratch and mar resistance, and distortion of appearance at weld lines and with complex parts such as those made with deep draw. Attempts to solve these problems have met with mixed success.
Producing a surfacing film with paint like appearance has experienced limited success due to problems in processing films onto articles and unattractive economics for films in replacing paint. Fashioning a surfacing (skin) film system that can replace paint appearance is challenging since the film is required to meet many specifications including appearance that is similar to paint in both solid and metallic colors. In metallic paint application, a special effort must be made to control the size of the effect particles and the particles' orientation in painted surfaces in order to exhibit the desired metallic appearance. Flat or higher aspect ratio (length to thickness) effect particles in paint formulations are applied in ways to obtain a flat or parallel orientation with the surface. A variable characterizing this particle orientation in paint is called flop, and is calculated from color measurements (L values) obtained at different angles from the light source. Duplicating this metallic appearance inexpensively with a polymer surface skin system that has the other necessary surface attributes of high gloss, durability in outdoor exposure, chemical resistance, impact resistance, layer adhesion, temperature resistance and other properties has met very limited success based on a very small decorated surface market share for plastic colored skins.
Decorative composite surfacing films made from a liquid solvent or dispersion system such as those disclosed in U.S. Pat. Nos. 4,810,540; 4,931,324; 4,943,680; and 5,342,666 have been used. Dry paint transfer products such as those taught in U.S. Pat. No. 5,707,697 have been used. U.S. Pat. No. 5,985,079 teaches melt extrusion coating as a zero-solvent approach to clear coat production and co-extrusion as an approach to base coat/clear coat production for certain colors. EP 0 949 120 A1 presents a flexible, weatherable decorative sheet material that has an extruded base layer with a clear outer layer of extruded film as an overlay. A color adjustment layer of printing ink can be included between the base layer and the clear coat.
Reissue of U.S. Pat. No. 5,514,427 (Re. 36,457) purports to solve the problems presented by the PVC and films such as the Tedlar® films marketed by E.I. du Pont de Nemours and Company through the use of a substantially molecularly unoriented cast polymer film prepared by liquid casting methods. Typically these liquid cast films require multiple step processes to provide sheet attributes suitable for thermoforming and adhesion properties for injection cladding, as surface skins that provide a paint-like appearance. Often in these films, the polymer, pigment and effect particles are cast onto a high gloss film from a solution followed by solvent evaporation. In other film constructions, the pigment and effect particles may be printed onto the surface in order to provide the desired metallic effect orientation and appearance such as provided by a paint. Often though these films are not commercialized due to uneconomical cost in materials or processing or deficient attributes such as appearance degradation after thermoforming due to the thin pigment carrying layer or the thin pigment layer streaking after elongation.
Another approach has been to make a “solid” part with molded-in color. Bexloy®W automotive engineering resin, a blend of ionomer and polyethylene sometimes reinforced by glass fiber, marketed by E.I. du Pont de Nemours and Company, for instance, has found increasing use in molded parts such as automobile bumpers. Solid color can be incorporated into the material, but success in incorporating metallic colors has been limited. Also, paint adherence to Bexloy®W resin is poor and paint application that requires use of high temperature paint baking ovens (Original Equipment Manufacturing “OEM” Painting) is not feasible since Bexloy®W lacks suitable high temperature properties. To enhance mar resistance, a light grain is typically applied to this material resulting in a loss of “Distinctness of Image” (DOI), a key index used to evaluate the perceived quality of an exterior finish in the automotive industry.
Another “solid” material that has been used is Surlyn® Reflections Series® resins, an ionomer-polyamide blend, marketed by E.I. du Pont de Nemours and Company. Molded parts made from this engineering material retain important performance characteristics of the Bexloy®W, have high gloss exhibiting DOI's at least comparable to the best of paint finishes on smooth or “Class A” surfaces, particularly DOI's over 80 and as high as 90 to 95. Solid and metallic colors can be incorporated and parts can be painted. High temperature properties are sufficient to permit OEM Painting without the need for special jigs or hangers to maintain part shape during the bake step. See U.S. Pat. No. 5,866,658.
By molding in color, certain capital, operating, and pollution abatement costs, particularly those associated with paint and solvent systems, can be eliminated. The solid parts have more durability and exhibit fewer defects as a result of weathering, chemical attack, and chipping than painted parts in use. However, they can exhibit splay, ghosting, flow lines and, in the case of a flake or particle with an aspect ratio, “metallic flow lines” which are often objectionable flow induced visual imperfections that particles in the polymer highlight due to light reflection and scatter. Solid injection molded parts can be uneconomical since the higher value polymer that provides the desired surface attributes is typically much thicker than needed to provide just the attributes of the surface, and in many cases the entire thickness of the part may be the higher value polymer.
Japanese patent application (Kokai) No. SHO 58(1983)-155953, teaches the concept of making a laminated molding body with a polyolefin layer and a surface layer made from a metal salt of an ethylene-α,β-unsaturated carboxylic acid copolymer having a glossy surface after lamination. Although the reference teach generally that there are no special limitation on the method used for laminating the base layer (polyolefin) to the surface layer (ionomer) with or without an intermediate adhesive layer which included co-extrusion, the working examples deal exclusively with hot pressing a commercial grade ionomer film (Surlyn®A1652) to a 2 mm thick polyolefin sheet of polypropylene or ethylene-propylene block copolymer. Also, the fabrication of the case-shaped product involved preheating the laminated sheet and vacuum molding on the side opposite the die. No mention of multilayer, co-extruded, ionomer film or sheet and any advantage of the same is present in this prior art reference.